Heretofore, in the field of polymerization of dispersion resins, once a surface active agent, for example an emulsifier, was added to the resin in a polymerization process to provide a desired particle size or a stable dispersion, it was retained by the resin throughout its manufacturing life including end product use. Oftentimes, such agents imparted unfavorable properties. By way of example, in the emulsion polymerization of vinyl resins, relatively large quantities of emulsifiers, soaps, etc. are utilized. Although in emulsion polymerization, the finished product is a polymer latex which theoretically ca be coagulated, filtered to remove the polymer particles, washed to remove part of the surfactant and then dried, practically it is difficult to conduct such a process without using coagulation aids of various types which aids may impart unfavorable properties to the end products. Thus, in the common industry practice of spray drying the polymer latex, various emulsifiers, surfactants, etc., are deposited on the polymer particles surface, thus generally imparting unfavorable properties thereto. These deposits can and often do impart cloudiness or turbidity in films when the film is made from a plastisol. The surfactant type will strongly influence the viscosity of a plastisol made from the resin and often produce a value other than desired. Heat stability and color of the plastisols are also affected.
While numerous attempts have been made to remove the emulsifiers, etc., from various dispersed particles as by simply washing the same, most have encountered various technical problems. Moreover, the various proposals have been expensive and complicated. Accordingly, little has been done to remove the soap after the spray-drying operation.
Although various compounds have been added to a spray-drying solution to alter the surface characteristics of the dispersion resins, such processes require a large amount of such compounds in order to overcome the effects of the surfactant which were already present. Oftentime, it is not possible to eliminate the effect of the original surfactant.
U.S. Pat. No. 3,901,842 relates to coagulation of a vinyl polymer latex, centrifuging the same to form a polymer wetcake and then redispersing the wetcake by use of a redispersant such as a polyacrylate. Thereafter the redispersed wetcake is dried in a spray-dryer.
U.S. Pat. No. 4,292,424 to Huddleston et al relates to the production of vinyl dispersion resins by means of emulsion polymerization and the recovery of the resins by a process which includes coagulating the latex to form a filtering sludge, passing the sludge to a pressure filter to separate the high solids, forming a friable wetcake, rinsing the wetcake with proper agents to neutralize the same and removing undesirable residues. Pressure in the filter is applied to the rinsed wetcake to increase the solids content thereof. The wetcake is then broken into particles, dried and ground to a proper size in one step in a fluid energy mill.
U.S. Pat. No. 4,207,158 relates to a process for dewatering a suspension of solids utilizing an electrically augmented vacuum filtration apparatus.
U.S. Pat. No. 4,331,525 relates to a process and apparatus for the recovery of suspended solids from a liquid medium. The liquid medium containing suspended solids is circulated through an electrolytic cell and an ultrafiltration unit, the suspended solids being removed from the liquid medium as a uniform particulate mass of low liquid content while a proportionate amount of the liquid and dissolved components such as surfactants is removed through ultrafiltration to avoid a dilution of the liquid medium.
European Patent Application No. 0,028,837 relates to a processing apparatus for recovering suspended solids from a liquid medium. An electrolytic cell as well as an ultrafiltration unit is utilized.
U.S. Pat. No. 4,134,820 relates to an apparatus for removing a wetcake from an anode in an electrofiltration process.
U.S. Pat. No. 4,107,026 relates to a method and apparatus for dewatering suspended matter and includes the use of vacuum filtration.
U.S. Pat. No. 4,246,039 is similar to U.S. Pat. No. 4,107,026 and also relates to the use of electrofilitration.